Induction-motor control.



PATENTED MAR. 24, 1908.

E. I. W. ALEXANDERSKMa INDUCTION MOTOR GGNTROL. APPLIOATIOK mum 2.1.1900.

mz e/vtaf Ernst F W Aexa/vc ersan a, Atty l V/tness as ductiori motors,

U ITED STATES PATENT OFFICE.

ERNST F. W. ALEXANDERSON, OF SOHENEGTADYT, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK.

, INDUCTION-MOTOR CONTROL.

' .application filed March 7,

To all whom it may concern:

Be it known that I, ERNST F. W. ALEX;

ANDERSON, a subject of the King of Sweden,

residing at Schenectady, in the count of 6 Schenectady and State of New York, aveinvented certainnew and useful Improve-' ments in Induction-Motor Control, of which the following is a s ecification. I

My invention re ates to the control of inand its object is to provide a novel method of, and means for, controlling such motors, whereby they may be 0 rated eflicientlyat different speeds and t eir.

speeds increased step-by-step in assimple a manner as is pos'sib c with a direct-current motor. It has. been proposed heretoforeiso to arrange induction motors as to adapt them for connection for different polenumbers, thereby obtaining av plurality of differ out speeds. This has been accomplished both by varying. the connections of a single winding and by providing the motor with a plurality of separate windings of different pole numbers. If the secondary member is coil-wound, and not of the squirrel-cage type,

both rimary and secondary must be arrangeclfor connection for either speed. Such an arrangement gives a plurality of fixeds eeds, but not means for shifting gradually t e speed at which the motor tends to run at no load. I a

1 My invention relates to motors having 7 .5 both primary and secondary members adapted for connection for different pole numbers, and consists in supplying current to both sets of connections simultaneously and varying the relative impedance of the circuits 1 formed by the two sets of secondary connections.' By supplying current to both sets of 40 primary conr rations simultaneously, a speed is produced somewhere between the two speeds corresponding to the two different pole numbers. The current in the connections In the smaller number of oles attempts to pull the motor up to the .lgher of the two liitniting speeds, but when the speed corresponding to synchronism for the greater number of poles is passed, the current in that set of connections exerts a negative torque,-

or in other words, produces a. generator action which tends to ret rn current to the line. The resultant torqrFe is the difference between the positive torque produced by the current in the connections corresponding to 56 the-smallerjnuniber of poles and the negative Specification 01 Letters Patent.

' Patented Mm 24, 1908. 1906. saw naaoasto.

' torque roduced in the other set of connections. y varying the relative impedances of the two secondarycircuit's, these torques may be varied relatively to each other, so that consequently the speed of the motor for :a' given torque may-be varied and may be -made to assume any desired value between the two limiting speeds. Q

' My invention further comprises certain arrangements of controlling means adapted for the convenient practice of the control above described.

lreferencefto the accompanying draw'ings,in 'which Fi duction motor arrang or control in accordance with my invention and-Fig. 2 is an explanatory diagram, i

I Referring first to Fig. 2, the curves a and 6 represent speedtorqne characteristics of a motor connected bersg The ratio of the two pole numbers for the curves shown thefigure may be considered for example as representing the curves of a motor connected ,for eight poles and four poles, respectively. The curve a is shown continued beyond the point 1- re resentin synchronous speed, beyond whic 1 point t tive, indicating the of connection iso erative, the speed-tor ue characteristic of tile motor is represented y the corresponding curve a or b, with the limiting speeds,that is, thepoints of zero torque, at 1 and 2, resp ectively. Now, if it is desired to obtain speeds between .1 and 2, this can be accomplished by connecting the motorfor both pole numbers at the same time and varying the relative impedances in the, secondary circuits. It is well underinotor modifies the the slope,or in other words, shiftingrthe point of maximum torque back to a lower speed. Thus, for instance, assume that voltage is being supplied to both sets of primary connections and that sufficient resistances are included in the two secondary circuits so as to modify the speedtorque charactaristicslfrir the two ,pole numbers, as reprse'nte'd bythe curve a andb. If these two curves arelconsidered, it willbe e torque becomes negawell-known generator action above synchronism. If only one set v fMy invention will best be understood by for two different pole num- .in this figure 2 to l, and

stoodin tlie art that inserting a noninduc-' tlveresistance 'in the circuit of an induction the positive torque at this speed,

seen that the points where the two curves. are intersected by the vertical line 3 are equidistant from the speed axis. In other words, A due to the current in the tour-pole connections, is equal to the negative torque due to the current 1n as to make thespeed-torque characteristic as indicated by the curve a", while at the same time the resistance in the tour-pole sec ondary circuit is decreased so as to make the s eed torque characteristic as indicated by t e curve 21 then the speed at which the positive and negative torques are equal is that indicated by the vertical line 4 so that the point where this line cuts the speed axis becomes the limiting s eed, or point of zero torque. Obviously, .y further varying the relative values of the resistances in the two second ary circuits, as many other speeds as desired intermediate the points i and 2 may be obtained. Further, it will be seen that although at the intermediate speeds some energy is being wasted int-he resistances of the secondary circuits, at the two limiting speeds, that is, when either secondary circuit is short-circuited, the motor operates with normal eihcienc-y.

In view of the above explanation, the connections, as shown in Fig. 1, will be readily understood.

A and 13 represent two primary windings connected for eight poles and tour poles, respectively. The particular arrangement of these windings-for obtaining these pole numbers forms no part of my invention, and will be readily understood by those skilled in the art. Furthermore, although I have indicated two distinct windings for obtaining the two pole numbers, this arrangement is not essential to my invention in its broader aspect. The two primary windings are shown connected in parallel to the source of three-phase current indicated by the linewires C.

A and B represent the secondary windin gs of the motor, which are also respectively arranged for eight poles and tour poles.

R R represent resistances, each of which has its opposite terminals connected to the two secondary windings respectively. A short-circuiting switch member S is arranged to connect successively different points of each resistance to corresponding points on the other resistances. With the switch member in an intermediate position, as shown, the four-pole secondary windin B is I connected in Y in closed circuit'wit h the upper portions of the resistances, while the elg t-pole winding is similarly connected with the lower portions of the resistances in circuit. As the switch member S is moved upor down, tlieresistance in circuit with each secondary winding is siinultaneouslv and oppositely varied. With the switch member in either extreme position, one of the secondary windings is sliort-circuited on itself, while the other has all the resistances in circuit with it'.

Although I have shown and described a motor arranged for only two pole-numbers, it will be understood that my invention is not limited to this particular application, but may be used to secure gradual variations from one speed tov anotherin a motor ar ranged for connection for any number 0 poles.

I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invent-i on. i

I do not claim broadly the method of opcrating an induction motor at varying speeds, consisting in establishing two sets of connections adapted to produce operation at two different speeds, supplying current to both sets of connections simultaneously, and

varying the relative torque produced thereby, s1nce I believe that K. A. Pauly is entitled to prioritv of invention on the said method,

'thus broadly stated What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The method of controlling an induction motor having both primary and secondary members adated for connection fordiflerent pole num ers, which'consists insupplying current to both sets of primary CODJ1C- tions simultaneously, and varyin the relative impedances of the circuits Formed by the two sets of secondary connections. I

2. The method of controlling an induction motor having both primary and secondary members adapted for connection for different pole numbers, which consists in supplying current to both sets of primary connections simultaneously, and varying simultaneously and oppositely the impedances of the circuits formed by the two sets of secondary connections.

3. The method of operating at varying speeds an induction motor having two windings of diiterent ole'numbers on both primary and secon ary members, which consists in suppl ing current toboth primary windings and varying the relative impedances of the circuits of the secondary windings.

4. The method of operating at varying speeds an induction motor having two windings of dilerent ole numbers on .both primary and socon ary members, which consists in supplying current toboth primary windings and varying simultaneously and ceases the secondary windings.

' circuits connections.

the relative imped ances 5. In combination, an induction motor liavii'ig; both primary and secondary inein bers adapted for connectionfor different pole numbers, means for supplying current to both sets of primary connections si nuita neously, and means for yarying the relative impedanccs oi? the circuits formed by the two sets oi secondary connections.

6. In combination, an induction motor having both primary and secondary memhers-adapted for connection for diflerent pole numbers, means for supplying current to both sets of primary comiections si1nulta-- neously and. means for varying simultaneousl. a d conositely the impedances of the cruise ution, an induction motor of primary and secondary ercnt pole numbers, in ans for supplying rent to both piimary indings simultaneously, and means for varying in the circuits of the two secondary windings.

8. In combination, an induction motor having two sets of primary and secondary windi of different pole numbers, means for suy pying current to bothv primary wind iugs sinmltanoously, and switching means in circuit with both secondary windings ar ranged to vary the relative impedances in the circuits of said. windings.

by the two sets of secondary 9; In combination, an induction motor .liaving two sets of primary and secondary windings of difierent pole numbers, means for supplying currentto bot 1 primary windings simultaneously, and switching means in circuit with both secondary windings arranged to vary simultaneously and oppositely the impedances of the circuits of said windings. i

10. In combination, an induction motor havig twosets of primary and secondary windings of different pole numbers, means for supplying current to both primary windings simultaneously, a non-inductive resistance, and means for inserting variable por tions of said resistance in cn'cuit with either secondary winding.

11. In combination, an induction motor having two sets of primary and secondary polyphase windings of diflerent pole numbers, means for supplying current to both primary windings, a plurality of resistances, coni'ieotions from opposite terminals of each resistance to tlie'two secondary windings respectively, and a short circuiting switching member arranged to connect successively different points on each resistance to corresponding points on the other resistances.

In witness whereof, I have hereunto set my hand this 6th day of March, 1906.

ERNST F. W. ALEXANDERSON.

Witnesses:

BENJAMIN B. HULL, HELEN 'Onnonn. 

